Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 88: Electronic structure II

O 88.4: Talk

Friday, March 30, 2012, 11:15–11:30, MA 043

Co thin films on Cu(001): dispersion and spin polarisation of the unoccupied quantum well state — •Martin Ellguth, Christian Tusche, Aimo Winkelmann, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle

Co thin films on Cu(001) are a thoroughly investigated material system, where a surface state is present and quantum well states occur in the unoccupied part of the band structure. Using our momentum microscope, we have measured energy-resolved momentum images in two-photon photoemission (2ppe: hν = 3.1 eV) using 400-nm-photons from a frequency doubled Ti:Sa laser. The momentum imaging principle yields the full k_||^→-space of photoelectrons in a single measurement. We assemble such images over a range of kinetic energies and select an energy-vs-k_||,1 cut from the 3-dimensional dataset to visualize the dispersion relation of the unoccupied quantum well states in 2ppe depending on the film thickness (3 to 11 monolayers).

For a selected initial energy of 350 meV below the Fermi level, we obtain a spin-polarised version of such an image by placing a recently developed 2-dimensional imaging spin detector¹ into the electron beam path. We observe a spin polarisation of 0.5 for those k_||^→, where the resonant excitation via the quantum well state yielded an increased intensity and 0.45 in the remaining k_||^→-regions.

[1] C. Tusche, M. Ellguth, A.A. Ünal, C.-T. Chiang, A. Winkelmann, A. Krasyuk, M. Hahn, G. Schönhense, J. Kirschner, Appl. Phys. Lett. 99, 032505 (2011)